Smart Grafting of Lanthanides onto Silica via N,N‑Dialkylcarbamato Complexes

The
grafting and the postgrafting functionalization of lanthanide ions
on commercial amorphous silica have been herein carried out by using
as a precursor the terbium N,N-dibutylcarbamato
derivative [Tb­(O2CNBu2)3]. The reaction
of the complex with the surface silanols involved only a fraction
of the carbamato ligands. The following protolytic substitution of
the residual carbamato ligands was carried out by exploiting the Brønsted’s
acidity of the β-diketone dibenzoylmethane (Hdbm), in view of
the antenna effect of the β-diketonato groups, which are commonly
used in lanthanide photoluminescence studies. The reaction proceeded
at room temperature in a clean and easy way affording the introduction
of the chosen functionality in the lanthanide coordination sphere.
The same procedure has been followed by using as a precursor the X-ray
characterized heterometallic N,N-dibutylcarbamato complex [NH2Bu2]2­[Ln4(CO3)­(O2CNBu2)12] (Ln = Eu, Tb, Tm). In both cases, X-ray photoelectron
spectroscopy evidenced the chemical implantation of the lanthanide
ions on the silica surface, and photoluminescence studies pointed
out the potentiality of the proposed synthetic approach in the preparation
of highly luminescent materials.

本研究中，采用作为前体的铽 N,N-二丁基羰基衍生物 [Tb-(O2CNBu2)3]，实现了镧系离子在商用非晶态二氧化硅上的嫁接及其后嫁接功能化。该复合物与表面硅醇的反应仅涉及部分羰基配体。通过利用 β-二酮二苯甲酰甲烷（Hdbm）的 Brønsted 酸性，针对 β-二酮酸根基团的辐射效应（β-二酮酸根基团常用于镧系离子光致发光研究），对残留的羰基配体进行了以下原位取代反应。该反应在室温下进行，过程洁净且简便，成功引入了所选功能基团至镧系配位域中。采用作为前体的 X 射线表征的杂金属 N,N-二丁基羰基复合物 [NH2Bu2]2[Ln4(CO3)(O2CNBu2)12]（Ln = Eu, Tb, Tm）亦遵循相同程序。在两种情况下，X 射线光电子能谱证实了镧系离子在二氧化硅表面的化学植入，而光致发光研究揭示了该合成方法在制备高发光材料方面的潜力。